Water-Resources Investigations Report 84-4201

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Abstract

Groundwater in Michaud Flats, southeastern Idaho, is developed extensively for irrigation and industry. Extensive clay beds overlie the Bighole Basalt and Sunbeam Formation, which yield most of the water for irrigation and industrial wells; artesian aquifers in these rock units have heads below land surface and near those in the shallow water-table aquifer in the overlying Michaud Gravel. Transmissivities in artesian aquifers range from 19,6000 to 444,000 feet squared per day. High levels of arsenic were detected in groundwater in the Flats in 1972. During 1982, concentrations of arsenic twice exceeded the recommended drinking water limit of 50 micrograms per liter. Concentrations of other chemical constituents were generally within drinking water limits. Stable-isotope data suggest more than one source of aquifer recharge and indicate some mixing between waters from industrial ponds and local groundwater. Management alternatives are being implemented by two industries for control of groundwater contamination. These include reduction of effluent, installation of liners and leachate recovery systems in ponds, and removal and reclamation of precipitates in old slurry and evaporation ponds. Six sites will be monitored through 1985 to determine changes in groundwater chemistry and migration of contaminants. (USGS)

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